The present invention relates to a method of controlling fuel supply to an internal combustion engine, and more particularly relates to a method of controlling fuel supply to an internal combustion engine comprising the steps of calculating a basic value for fuel supply to the engine from fundamental operational parameters of the engine, calculating an adjustment value for this basic value, and adjusting the basic value according to the adjustment value to obtain a final control output value.
In FIG. 1 of the accompanying drawings is shown a timing chart for calculation of a final control output value which, in this case, is a value representing the amount of fuel injection for an internal combustion engine. The amount of fuel injection is determined by calculating a basic value for fuel supply, T.sub.p =k Q/N, from fundamental operational parameters of the engine; the amount of flow of intake air, Q, into the engine, a constant k and the rotational speed of the crankshaft, N, and adjusting the basic value according to an adjustment value which depends on the output of an oxygen sensor, not shown, which senses the concentration of oxygen in the exhaust gas; the opening of a throttle valve, not shown, provided in an intake air passage to the engine; and the temperature of the engine. Thus, fuel is supplied to the engine according to the final control output value once for each rotation of the crankshaft. In FIG. 1, it is assumed that the engine is a 6-cylinder type engine. A crank angle signal 10 is shown as consisting of pulses of R.sub.1, R.sub.2, R.sub.3, R.sub.4 . . . , which are sequentially produced at crankshaft rotational intervals of 120.degree.. The adjustment value is calculated once for each rotation of the crankshaft, at time periods A.sub.1 and A.sub.2. A calculation start signal 12 is shown as being a clock pulse signal containing clock pulses T.sub.1 . . . T.sub.11, but could alternatively be a signal synchronized with the crank angle signal. Calculation of the basic output data, shown by 13, is started, for each of the time period shown as B.sub.1, B.sub.2, . . . B.sub.11, when each of the pulses T.sub.1, T.sub.2 . . . of the calculation start signal 12 is received. A fuel injection valve drive signal 14 is shown as consisting of pulses C.sub.1, C.sub.2, one being produced for each rotation of the crankshaft. The latest completed basic output data obtained at time periods B.sub.1 and B.sub.9 are used for control of fuel supply, after correction by the latest adjustment value. Thus the latest adjustment value obtained at A.sub.1 is used for correcting the output value at B.sub.9.
As shown in FIG. 1, to simplify the structure of the control device used, the timing of R.sub.1 and the start of A.sub.1 and C.sub.1 are selected to be the same, and the timing of R.sub.4 and the start of A.sub.2 and C.sub.2 are selected to be the same.
The problem with the above described method according to the timing chart shown in FIG. 1 is that the adjustment value obtained at A.sub.1 is calculated one full crankshaft rotation before C.sub.2, and this value is used for adjusting the basic output value which defines fuel injection time C.sub.2, in the time period B.sub.9 starting from pulse T.sub.9. Thus the adjustment value is rather old, compared with the basic value which it is used to correct. During operation of the engine at substantially constant load and at substantially constant speed, no large effect due to this will occur on the operation of the engine, whereas, however, during a time when the operating conditions are fluctuating, it is difficult to maintain the air/fuel ratio at a proper constant value when the amount of fuel supplied to the engine is controlled on a feedback basis, for example, using information on the components of the exhaust gas.